Made ResolveReference public again as it is used by Swashbuckle

Author: darrelmiller

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -351,7 +351,7 @@ internal T ResolveReferenceTo<T>(OpenApiReference reference) where T : class, IO
         /// <summary>
         /// Load the referenced <see cref="IOpenApiReferenceable"/> object from a <see cref="OpenApiReference"/> object
         /// </summary>
-        internal IOpenApiReferenceable ResolveReference(OpenApiReference reference, bool useExternal)
+        public IOpenApiReferenceable ResolveReference(OpenApiReference reference, bool useExternal)
         {
             if (reference == null)
             {

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -508,6 +508,7 @@ namespace Microsoft.OpenApi.Models
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiServer> Servers { get; set; }
         public System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiTag> Tags { get; set; }
         public Microsoft.OpenApi.Services.OpenApiWorkspace Workspace { get; set; }
+        public Microsoft.OpenApi.Interfaces.IOpenApiReferenceable ResolveReference(Microsoft.OpenApi.Models.OpenApiReference reference, bool useExternal) { }
         public System.Collections.Generic.IEnumerable<Microsoft.OpenApi.Models.OpenApiError> ResolveReferences() { }
         public void SerializeAsV2(Microsoft.OpenApi.Writers.IOpenApiWriter writer) { }
         public void SerializeAsV3(Microsoft.OpenApi.Writers.IOpenApiWriter writer) { }